Recently, demand for a secondary battery is increasing in various industrial fields, such as cellular phones, notebook computers, small domestic appliances, automobiles, and bulk power storage systems. Therefore, research on improving the performance of a secondary battery is vigorously proceeding.
A secondary battery is composed of an anode prepared by using a carbon material or a lithium material, a cathode prepared by using a metallic oxide, such as LiNiO2 and LiCoO2, and an electrolyte located therebetween.
When charging a secondary battery, a lithium ion is de-intercalated from a cathode, is moved through the electrolyte, and then, is intercalated in an anode, thereby turning electrical energy into chemical energy and storing the chemical energy. When discharging a secondary battery, the reverse mechanism proceeds to supply electrical energy to an external circuit, and the lithium ion intercalated in an anode is again moved to the cathode. In other words, the electrolyte acts as a medium for carrying the lithium ion to be oxidized or reduced in the anode or the cathode within the battery.
At present, the electrolyte for a secondary battery is mainly limited to a liquid electrolyte. The liquid electrolyte has an advantage, that is, high lithium-ionic conductivity, but it is mainly composed of flammable organic materials, and thus may be dangerous, such as, from a leakage, or a fire or explosion at high temperature.
Therefore, in the case of a small battery, or a secondary battery used for automobiles or power storage, there may be a danger to a person's health from a fire or an explosion.
The above-described problem associated with a liquid electrolyte may be solved by instead employing a safer, inorganic-based solid electrolyte. The solid electrolyte is divided into an oxide-based and a sulfide-based solid electrolyte. The electrostatic binding energy of sulfur is lower than that of oxygen, and thus, a sulfide-based solid electrolyte exhibits higher lithium-ionic conductivity as compared with an oxide-based solid electrolyte.
In addition, since a sulfide-based solid electrolyte is stable over a wide range of voltages, a sulfide-based solid electrolyte can be used to be used as a high-voltage electrode material that is difficult to be used for conventional liquid electrolyte.
The prior art discloses a sulfide-based crystallized glass having excellent economic feasibility, in which sulfide-based crystallized glass exhibits high lithium-ionic conductivity at room temperature, and can be industrially manufactured by promoting a decrease in the temperature required for a heat-treatment and a decrease in the amount of lithium included in electrolyte.
However, since a sulfide-based solid electrolyte has still low lithium-ionic conductivity as compared with a liquid electrolyte, more research into developing solid electrolytes having improved lithium-ionic conductivity is required.
The above information disclosed in this Background section is only for the enhancement of understanding of the background of the disclosure and therefore may include information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.